The present invention relates to a method and a device for washing machine parts having machine-finished spherical or cylindrical outer surfaces, e.g. balls or rolls for roller bearings, in connection with the manufacture thereof.
In the manufacture of roller bearings, washing, i.e. cleaning and degreasing, should be effected upon each finishing operation in order to prevent the transfer of dirt and finishing remainders from one operation to another. Moreover, one operation is often completed by a dimensional check or a surface inspection, which calls for clean surfaces to provide correct results.
The manufacture of rolls and balls is often performed in such a way that the parts have to be stored for a long time, and to avoid damage to the surface finish, rust protection is required. For a satisfactory rust protection a rust preventive has to be applied onto completely clean surfaces.
To obtain a perfect operation of the finished roller bearing, the balls or rolls have to be machined to an extremely high surface finish.
Thus, it is absolutely necessary to protect the washing goods against damage during the washing operation, e.g. by preventing the balls or rolls from hitting each other or other objects so as to cause damage to the finished surfaces. Therefore, during the washing operation, a certain minimum distance should be maintained between the parts to avoid surface damage.
By experience in the art of roller bearings, it has been found that the washing must result in a residual dirt content on the surfaces of less than 0.01 mg per cm.sup.2 of the bearing surface. Such a result is to be considered as a minimum requirement and, in continuous service, it must be even better irrespective of the condition of the parts before the washing operation.
The requirements of the washing method depend heavily on the preceding operation, e.g. turning, grinding, lapping or polishing. Likewise, the washing method and washing results are dependent on the surface quality (profile depth) of the washing goods.
Regarding the choice of solvents for the washing operation, requirements for an increased environmental and personal health protection have caused the water-based washing methods to be abandoned, since it is no longer permitted to discharge the used washing liquid directly into open water and, additionally the destruction or regeneration is highly energy consuming and costly. Furthermore, chlorinated hydrocarbons, such as tri- and perchloroethylene, must be avoided if possible, since they are suspected to cause cancer. Moreover, efforts are made to avoid freons which, as a matter of fact, are prohibited in certain states in the U.S.A., because of their effect upon the ozone layer surrounding the earth.
In view of the above-mentioned, it is desireable to provide a washing method which, on the one hand, is effective to such a degree that also other solvents, such as white spirit or the like, having per se a lower washing power, can be used with a satisfactory result, and, on the other hand, permits the use of solvents, which are per se, polluting or involving personal health risks, such as the above-mentioned chlorinated hydrocarbons and freons, by closed re-circulation of such solvents.